Method for centering capacitor in mold

ABSTRACT

A capacitor includes a pellet molded within a protective material and having a cathode termination surface at one end and an anode wire extending from the other end. The cathode termination surface is centered with respect to the longitudinal axis of the capacitor. The method includes centering the pellet body and a tear drop shaped conductive cathode element within a mold and molding a protective coating around them. After the molding is complete a portion of the tear drop shaped member is removed to create a cathode termination.

BACKGROUND OF THE INVENTION

The present invention relates to a capacitor termination and method for making same.

Presently known techniques for forming a cathode termination on a capacitor often result in off center cathode termination surfaces. These off center terminations can result in inconsistencies in the performance of the capacitors and is undesirable.

Therefore a primary object of the present invention is the provision of an improved capacitor termination and method for making same which permits the molding of a protective material around the capacitor pellet with a substantially uniform thickness.

A further object of the present invention is the provision of an improved capacitor termination and method for making same which results in a cathode termination that is centered with respect to the capacitor body.

A further object of the present invention is the provision of an improved capacitor having a low ESR.

A further object of the present invention is the provision of an improved capacitor termination and method for making same which is economical, efficient in operation, and simple in operation.

SUMMARY OF THE INVENTION

The foregoing objects may be achieved by a capacitor comprising a capacitor pellet having an anode end a cathode end, a front face, a rear face, first and second opposite sides, and a longitudinal pellet axis extending from the cathode end to the anode end. An anode wire is connected to and in contact with the pellet and extends outwardly from the anode end of the pellet. A quantity of conductive material is in electrical contact with the cathode end of the capacitor pellet. A molded material covers the pellet with a substantially uniform thickness and also covers a portion of the conductive material at the anode end of the pellet. The molded protective material leaves a portion of the conductive material uncovered to create and expose a cathode termination at the cathode end of the pellet. The cathode termination is approximately centered on the longitudinal axis of the pellet and faces axially away from the cathode end of the pellet. A cathode terminal covers and is in electrical contact with the cathode termination.

The method of the present invention comprises forming a capacitor pellet having a pellet anode end, a pellet cathode end, a pellet front wall, a pellet rear wall, first and second opposite pellet side walls, and a longitudinal axis extending between the pellet anode and cathode ends an anode wire is connected to and extends from the anode end of the pellet. A fluid conductive material capable of hardening is applied to the cathode end and portions of the pellet front wall, rear wall, first side wall and second side wall adjacent the cathode end of the pellet. The fluid conductive material creates a tear drop shaped conductive body having a tear drop point extending axially away from the cathode end of the pellet. The fluid conductive material is permitted to harden. A protective material is molded around the pellet and the conductive material to form a protective coating. A portion of the tear drop point and the protective coating are then removed to form an exposed cathode termination surface of the conductive body.

According to another feature of the invention the removing step further comprises forming the cathode termination surface into a flat surface facing axially away from the pellet cathode end.

According to another feature of the invention the removing step is accomplished by cutting or by grinding the tear drop point.

BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS

FIG. 1 is a sectional view of a capacitor made according to the present invention.

FIG. 2 is an elevational view showing the pellet, wire, and teardrop body of the present invention.

FIG. 3 is a simplified and partial semetric view of the molds used to produce the capacitor of the present invention.

FIG. 4 is a top plan view of the pellet positioned within the bottom mold member.

FIG. 5 is a sectional view taken along line 5—5 of FIG. 4.

FIG. 6 is a sectional view of the molded capacitor before the bottom portion thereof is removed.

FIG. 7 is a view similar to FIG. 6, but showing a prior art capacitor.

DETAILED DESCRIPTION OF THE PREFFERED EMBODIMENT

Referring to FIG. 1 the numeral 10 generally designates a capacitor made according to the present invention. Capacitor 10 includes a pellet 12 having an anode pellet end 14, and a cathode pellet end 16. An anode wire 18 is embedded in and extends from the anode pellet end 14 of pellet 12. Pellet 12 also includes a pellet front wall 20 (FIG. 5), a pellet rear wall 22, and opposite pellet side walls 24, 26. Surrounding the pellet 12 is a protective body 28 made of molded material which protects the integrity of the pellet 12. Numerous molding materials have been used, and they are preferably dielectric. However, persons skilled in the art may select a wide variety of protective molded materials without detracting from the invention. The preferred molding compound is manufactured by Dexter Corporation at 211 Franklin Street, Olean, N.Y. 14760, under model number MG 53 F.

The protective body 28 includes a pair of opposite side indentations 30, 32. Other side indentations are also formed in the protective body 28 and will be described hereafter. Surrounding the bottom of the pellet 12 is a cathode termination 34 made of a conductive material which may be silver, other metals, or conductive epoxy. A wide variety of these conductive materials are available and are used in the industry. The preferred conductive material for use in the present invention is a conductive epoxy sold under the Model No. 61445, by Metech, Inc., having an address of Rt. 401, Box 360, Elverson, Pa. 19520. The cathode termination 34 includes a downwardly presented cathode termination surface 36 which engages a cathode terminal cap 38 made of conductive material. Cathode cap 38 includes cap side walls 40 and a cap end wall 42. The wire 18 provides the anode termination for capacitor 10. A conductive anode cap 97 can be provided at the anode end so as to engage the wire 18 and provide an anode terminal for capacitor 10.

Referring to FIG. 2, the pellet 12 is shown in its form before being placed in the mold. Pellet 12 is formed by conventional press molding and sintering technique which are well known in the art. The pellet 12 is covered at its cathode end 16 by a tear drop shaped body 44 made of the above identified conductive material. Body 44 includes an upper portion 45 which surrounds the front, side and rear walls of the pellet 12 adjacent the cathode end thereof. Tear drop shaped body 44 also includes a tear drop point 46. In some cases there are multiple tear drop points 46.

The formation of tear drop shaped body 44 on the cathode end 16 of pellet 12 is accomplished by dipping pellet 12 into a reservoir of fluid hardenable conductive material, or alternatively by using a syringe. After application the conductive material is permitted to cure and harden.

The pellet 12 shown in FIG. 2 is positioned within a molding cavity formed by an upper mold 48 and a lower mold 54. Upper mold 48 includes an upper mold face 50 on its lower surface and a pair of spacing ribs 52 which protrude downwardly therefrom. Bottom mold 54 includes a bottom mold face 56 which faces upwardly. Cavity side walls 58, 60 and a cavity bottom wall 62 combine with the upper mold face 50 to form a molding cavity as shown in FIG. 5. The molding cavity includes an anode end and a cathode end.

A pair of L-shaped spacers 64 are positioned with upstanding legs 66 extending along the cavity side walls 58, 60 and with horizontal legs 70 extending along the cavity bottom wall 62. The upper edges of upstanding legs 66 are each provided with a tapered edge 68 (FIG. 5).

FIGS. 4 and 5 show the pellet 12 positioned within the mold. In this position the L-shaped members 64 extend from the cathode end 80 of the cavity toward the anode end 82 of the cavity, and terminate at a point spaced from but adjacent the cathode end 16 of the pellet 12 as can be seen in FIG. 4. The ribs 52 of the upper mold 48 extend longitudinally approximately the same distance from the anode end 80 of the cavity. As can be seen in both FIGS. 4 and 5 a substantially uniform space 72 is formed around all four sides of the pellet 12. The L-shaped pieces 64 and the ribs 52 engage the cathode end of the pellet, and specifically engage the tear shaped body 44 to center the pellet 12 within the cavity. While the ribs 52 and the L-shaped members 64 are used to center the pellet 12 within the cavity, other shapes and configurations of projections could accomplish the same result without detracting from the invention. The importance of centering the pellet 12 within the cavity is that when the molding process is complete there is a layer of protective material surrounding the pellet, and that layer of protective material is of substantially uniform thickness.

FIG. 6 shows the completed molded uncut capacitor body designated by the numeral 74. This capacitor body 74 is cut along a cut line 76 to remove a lower body portion 78 and to expose the cathode termination surface 36 that can be engaged by the terminal cap 38 as shown in FIG. 1.

The removal of the removed body portion 78 can be accomplished by cutting, grinding or other conventionally known means.

The completed capacitor 10 has a cathode termination surface 36 which is flat and which faces axially away from the cathode end of the pellet. It is also centered with respect to longitudinal axis of the pellet. This centering is accomplished by the molding process which utilizes the projections 52, 64 to center the pellet and the tear dropped shaped body 44 within the mold cavity.

FIG. 7 illustrates a prior art capacitor 84 made according to a prior art method for creating the cathode termination. The capacitor 84 includes a pellet 86 and an anode wire 88. A protective body 90 is molded around the pellet 86. At the cathode end of the pellet 86 is a conductive adhesive 92 which attaches a silver pin 94 to the pellet 86. A cut is made along cut line 96 and this cut exposes the silver pin 94 to create the cathode termination surface.

Neither the conductive adhesive 92 nor the silver pin 94 can be used as a means for centering the pellet 86 in the molded body 90. Without the use of the tear drop shaped body, this process is very difficult to center the pellet 86 in the molded body 90. Failure to properly center the pellet 86 can result in thin spots or even openings in the protective coating 90. In contrast the use of the tear drop shaped body 44 and the use of the projections 64, 52 to center the body within the mold cavity creates a termination which is centered with respect to the longitudinal access of the pellet, and which has a protective coating 28 of uniform thickness around the side wall of pellet 12.

In the drawings and specification there has been set forth a preferred embodiment of the invention, and although specific terms are employed, these are used in a generic and descriptive sense only and not for purposes of limitation. Changes in the form and the proportion of parts as well as in the substitution of equivalents are contemplated as circumstances may suggest or render expedient without departing from the spirit or scope of the invention as further defined in the following claims. 

What is claimed is:
 1. A method for making a capacitor comprising: forming a capacitor pellet having a pellet anode end, a pellet cathode end, a pellet front wall, a pellet rear wall, first and second opposite pellet side walls, and a longitudinal axis extending between said pellet anode and cathode ends; connecting an anode wire to said anode end of said pellet with said anode wire extending from said anode end of said pellet; applying a fluid conductive material capable of hardening to said cathode end and to lower portions of said pellet front wall, rear wall, first side wall, and second side wall adjacent said cathode end of said pellet to create a tear drop shaped conductive body having a tear drop point extending axially away from said cathode end of said pellet; permitting said fluid conductive material of said tear drop shaped conductive body to harden; placing said pellet having said conductive body thereon within a mold cavity having a plurality of walls provided with a plurality of projections extending inwardly therefrom into said mold cavity; engaging only said tear drop shaped conductive body with said plurality of projections so as to center said pellet within said cavity and create a substantially uniform space within said cavity around said front wall, said rear wall, and said first and second side walls of said pellet; introducing a molding material into said space within said cavity to form a protective coating of substantially uniform thickness around said pellet, and to substantially surround said tear drop shaped conductive body except where said projections engage said conductive body; removing a portion of said tear drop point and said protective coating to form an exposed cathode termination surface from said conductive body.
 2. A method according to claim 1 wherein said removing step further comprises forming said cathode termination surface into a flat surface facing axially away from said pellet cathode end.
 3. A method according to claim 2 wherein said removing step is accomplished buy making a cut through said dielectric material and said hardened conductive material to expose said cathode termination surface.
 4. A method according to claim 2 wherein said removing step is accomplished by grinding said tear drop point and said protective coating which covers said tear drop point.
 5. A method according to claim 1 and further comprising attaching a conductive cathode terminal over said cathode end of said pellet and in electrical contact with said cathode termination surface.
 6. A method according to claim 1 wherein said mold cavity includes an anode end free from said projections and a cathode end from which said projections extend, said step of placing said pellet within said mold cavity further comprising placing said cathode end of said pellet adjacent said cathode end of said mold cavity and placing said anode end of said pellet adjacent said anode end of said mold cavity.
 7. A method according to claim 1 wherein said mold cavity includes a top mold wall, first and second opposite side mold walls, and a bottom mold wall, said projections including a top projection, a first projection, a second projection, and a bottom projection extending from said top mold wall, said first side mold wall, said second side mold wall, and said bottom wall respectively, said method further comprising engaging said tear drop shaped body with said top, first, second, and bottom projections respectively to center said pellet within said mold cavity. 